The potential allelopathic (phytotoxic or beneficial) effect of barley, oat, and wheat straw mulches was evaluated on growth, mineral nutrition, and mycorrhizal status of black spruce seedlings, un...

Weeds are known to cause enormous losses due to their interference in agroecosystems. Because of environmental and human health concerns, worldwide efforts are being made to reduce the heavy reliance on synthetic herbicides that are used to control weeds. In this regard the phenomenon of allelopathy, which is expressed through the release of chemicals by a plant, has been suggested to be one of the possible alternatives for achieving sustainable weed management. The use of allelopathy for controlling weeds could be either through directly utilizing natural allelopathic interactions, particularly of crop plants, or by using allelochemicals as natural herbicides. In the former case, a number of crop plants with allelopathic potential can be used as cover, smother, and green manure crops for managing weeds by making desired manipulations in the cultural practices and cropping patterns. These can be suitably rotated or intercropped with main crops to manage the target weeds (including parasitic ones) selectively. Even the crop mulch/residues can also give desirable benefits. Not only the terrestrial weeds, even allelopathy can be suitably manipulated for the management of aquatic weeds. The allelochemicals present in the higher plants as well as in the microbes can be directly used for weed management on the pattern of herbicides. Their bioefficacy can be enhanced by structural changes or the synthesis of chemical analogues based on them. Further, in order to enhance the potential of allelopathic crops, several improvements can be made with the use of biotechnology or genomics and proteomics. In this context either the production of allelochemicals can be enhanced or the transgenics with foreign genes encoding for a particular weed-suppressing allelochemical could be produced. In the former, both conventional breeding and molecular genetical techniques are useful. However, with conventional breeding being slow and difficult, more emphasis is laid on the use of modern techniques such as molecular markers and the selection aided by them. Although the progress in this regard is slow, nevertheless some promising results are coming and more are expected in future. This review attempts to discuss all these aspects of allelopathy for the sustainable management of weeds.

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Effect of straw residues on black spruce seedling growth and mineral nutrition, under greenhouse conditions

Allelopathic Interactions and Allelochemicals: New Possibilities for Sustainable Weed Management

Numerous reports have been published on the occurrence, isolation, and characterization of phenolic compounds in plant‐soil systems. The low molecular weight phenolics are of great interest because of their effects as allelopathic compounds and plant growth regulators, and they have traditionally been considered as defense molecules in plant‐pathogen interactions. More recently, their role as signal molecules in plant‐microbe systems has become evident. Specific molecules can act either as inducers for virulent genes in plant‐pathogen systems, such as Agrobacterium, or as inducers and “repressors”; in Rhizobium‐legumc and probably other symbiosis. The overall regulation role of these compounds in compatible and incompatible host‐microbe interactions is discussed in this review.

Significance of phenolic compounds in plant‐soil‐microbial systems

Regeneration failure ofPicea abies in a subalpine bilberry-spruce forest was studied in relation to phenolic compounds, their occurrence and toxicity. Germination bioassays with natural leachates of bilberry (Vaccinium myrtillus) and spruce showed negative effects on root elongation of spruce seedlings. Growth bioassays on litter and humus demonstrated inhibitory effects of these organic layers.p-Hydroxyacetophenone, a spruce-specific metabolite, was isolated in spruce throughfall (10−6 M), in water extracts of litter (between 1 and 8 µg/g dry wt) and organic layer (less than 1 µg/g dry wt) in addition to tannins and several common phenolic acids. Potential relationships between vegetation cover and phenolic pattern of the soil are discussed, since organic layers under bilberry heath exhibited higher amounts of phenolic acids and tannins than those under spruce.p-Hydroxyacetophenone and caffeic acid reduced, even at 5 × 10−5 M, spruce seedling growth, especially root development, with additive effects for these two monomers. Autotoxicity involving spruce trees and allelopathy of understory species, mediated byp-hydroxy-acetophenone and other phenolic compounds, including tannins, deserves further attention in regeneration studies.

Allelopathic potential in bilberry-spruce forests: Influence of phenolic compounds on spruce seedlings.

During the past decade, considerable research efforts have been devoted towards non-chemical weed control. Some of these efforts have been directed towards the control of forest weed species. Non-chemical control of forest vegetation encompasses many approaches and techniques and only a few of them are discussed in this paper. Three major and promising research areas are identified: (1) allelopathy, (2) microbially produced phytotoxins, and (3) bio-control. Each of these weed management strategies is briefly presented and discussed using examples from the forestry literature.

Some future directions for biologically based vegetation control in forestry research

Allelopathy is currently gaining importance in Quebec as a factor of ecological significance However, there are few reports on the phenomenon Most of the work was done in forestry and surprisingly little in agriculture Research in allelopathy in Quebec was initiated in 1974 as part of a project on the ecology of balsam fir (Abies balsamea (L) Mill) and balsam poplar (Populus balsamifera L) at the Faculty of Forestry and Geodesy of Laval University (Quebec city) Then, the research was orientated on (1) the adverse allelopathic effect of forest weed species on regeneration and (2) the allelopathic control of competing species in forest plantations

Effect of straw residues on black spruce seedling growth and mineral nutrition, under greenhouse conditions

Citations

Allelopathic Interactions and Allelochemicals: New Possibilities for Sustainable Weed Management

Significance of phenolic compounds in plant‐soil‐microbial systems

Allelopathic potential in bilberry-spruce forests: Influence of phenolic compounds on spruce seedlings.

Some future directions for biologically based vegetation control in forestry research

Allelopathy in Quebec forestry - case studies in natural and managed ecosystems